The most common type of radiation therapy for the treatment of cancer is external beam radiation therapy (“EBRT”). For this treatment, an accelerator is used to generate and precisely deliver relatively high-energy particle or photon beams from outside the body into the tumor. There are a variety of EBRT technologies, with the type of radiation used falling into two general categories: (1) ionizing particles such as protons, ions, electrons, etc., and (2) ionizing photons such as relatively low-MeV gamma rays or X-rays. Ionizing photons are the more common type of radiation employed for EBRT. For particle beam radiation therapy, in addition to protons, carbon ions and electrons, other types of particle beams used or being investigated include helium, oxygen, neon and argon ions, as well as low-energy neutrons (e.g., slow to thermal neutrons). Low-energy neutrons are used, for example, in boron neutron capture therapy (“BNCT”) and gadolinium neutron capture therapy (“Gd-NCT”).
For both particle and photon EBRT, there are a variety of delivery methods, including intensity modulated radiation therapy (“IMRT”), intensity modulated proton therapy (“IMPT”), three-dimensional conformal radiation therapy (“3D-CRT”), image guided radiation therapy (“IGRT”), volumetric modulated arc therapy (“VMAT”), pencil-beam spot scanning, pencil-beam raster scanning, helical-tomotherapy, stereotactic radiosurgery (“SRS”), stereotactic body radiation therapy (“SBRT”), fractionated stereotactic radiotherapy (“FSRT”), spatially fractionated grid radiation therapy (“SFGRT”), ultrahigh dose-rate flash therapy (“FLASH”), intraoperative radiation therapy (“IORT”), boron neutron capture therapy (“BNCT”), gadolinium neutron capture therapy (“Gd-NCT”), etc.